This invention relates to electrical overload fuses in general and more particularly to an electrical overload fuse with a fusible link and quenching baffles of electrically conductive material.
As is well known, a fuse has as its purpose disconnecting part of a network or an electrical load in case of an overload or a short circuit. The fusible conductor is designed so that it melts as soon as the conductor current reaches a predetermined limit. By the special mechanical design of the fuse, the arc is forced to assume an operating voltage which is higher than the driving line voltage.
In the known fuses, the fusible conductor has essentially two purposes, namely, the current carrying function for the current flowing during normal operation and, for an overcurrent, which must likewise be carried for a certain period of time in the case of a disturbance or short circuit. It also has the current interrupting function which is obtained by a sufficiently large countervoltage. The two functions, however, place contradictory requirements on the fusible link, which, for higher voltages, leads to relatively complicated shapes of the fusible conductor.
A sufficiently high arc voltage can be produced by the fusible link, after it has melted through, only with a correspondingly great length. This, however, means a correspondingly large voltage and power drop during normal operation. In order to reduce this voltage drop, fusible links with several constrictions have been used. This design, however, raises a further problem, namely, the simultaneous melting of all constrictions (U.S. Pat. No. 1,946,553).
But even with this known design the voltage drop is still several tenths of a volt. In systems with a larger number of such fuses, for instance, in static converters with thyristors, with each of which a fuse is associated, a considerable amount of dissipation loss is therefore generated which must be removed as heat.
The problem of designing the fuse so that its voltage drop is small during normal operation and so that it is, at the same time, able to build up a large countervoltage which acts as the quenching voltage for interrupting the current, therefore arises.
In one known embodiment of a fuse, quenching baffles of electrically conductive material are therefore provided having flat sides extending transversely to the longitudinal direction of the fusible conductor and arranged one behind the other in the longitudinal direction thereof. As the fusible conductor melts, partial arcs are produced between the quenching baffles. Alternating with the quenching baffles are spaces in the form of hollow cylinders of a material which gives off a gas which acts as a quenching gas under the action of the arc. The fuse must therefore be pressure proof. The sum total of the individual partial arcs acts as a quenching voltage. The quenching baffles extend perpendicular to the direction of the fusible conductor and are arranged one behind the other in the direction of the fusible conductor. For higher switching voltages, especially above 1000 volts and with a correspondingly large number of quenching baffles, a relatively large design of the fuse is obtained.